Goods and other items may be tracked and identified using a radio frequency identification (RFID) system. The RFID system includes an RFID tag, which is typically placed on the item to be tracked. The RFID tag is a small transponder that can be read by an RFID reader (also referred to as an RFID interrogator). The reader includes a transceiver and an antenna. The antenna emits electromagnetic (EM) waves generated by the transceiver, which, when received by the tag, activate the tag. Once the tag has been activated, the tag communicates using radio waves back to the reader, thereby identifying the item to which the tag is attached or is otherwise associated with. In one form of RFID, the tag modifies and reflects the waves emitted by the reader, using the modified and reflected waves to communicate with the reader. In another form of RFID the tag emits a radio signal which is detected by the reader.
The reader may be a fixed or mobile device that transmits a radio signal which may be intercepted by the tag. When the tag encounters the radio waves, the tag detects the signal and is activated. Data encoded in the tag can then be transmitted to the reader for further processing. This system allows for quick and easy identification for a large number of items by simply passing them through the scope of a reader. This system will also identify items on which a tag is not exposed, such as items in which the tag is located internally. Further, the reader can read multiple tags very quickly, such as items passing by the reader while the items are on a conveyer belt.
There are three basic types of RFID tags. A beam-powered tag is a passive device which receives energy required for operation from the radio waves generated by the reader. The beam powered tag rectifies an EM field and creates a change in reflectivity of the field which is reflected to and read by the reader. A battery-powered semi-passive tag also receives and reflects EM waves from the reader, however the battery powered tag includes a battery to power the tag independent of receiving power from the reader. An active tag actively transmits EM waves which are then received by the reader.
Applications of RFID systems typically involve a reader identifying a tagged object. In many cases, the value of this information is that it provides a reference that the tagged item was at a particular location, at a particular time. To identify the location of the tagged item, it is assumed that the location of the reader is known. If the reader location is uncertain, some applications of RFID can be compromised. For example, anti-theft or inventory control applications of RFID assume that a reader is near a particular door or path, or at a specific location. In such an application, if the reader is unexpectedly moved, or if the reader malfunctions, there may be adverse results. For example, the reader owner may falsely assume that a particular doorway is being covered by the reader, or the reader may report an incorrect location for an object. In another situation, the reader may become shielded or damaged in some way, so that the coverage area of the reader becomes greatly diminished without notification to the network, and all or some tags pass by the reader without being detected, either intermittently or for an extended period of time.